1. Field of the Invention
The present invention relates to a process for the vapor phase oxidative bromination of aromatic compounds using a metal catalyst on a support such as a zeolite.
2. Discussion of the Background
The bromination of aromatic compounds is traditionally carried out by electrophilic substitution reactions using aromatic substrates such as benzene or naphthalene. The most common catalysts are the bromides of iron or aluminum although many other catalysts including iodine are effective. These reactions are generally known as Friedel-Crafts reactions.
Halogenation of aromatic compounds can also be carried out by an oxidative halogenation process. Vapor phase oxidative chlorination of aromatics is a commercial process and has been described in U.S. Pat. Nos. 1,963,761; 3,303,223; 3,389,186 and 3,644,542. In contrast, the vapor phase oxybromination of aromatics has received little attention, although liquid phase oxybromination is known. See for example U.S. Pat. No. 4,380,682 which discloses the oxybromination of aliphatic hydrocarbons by first performing a non-selective oxyhalogenation given intermediate partially halogenated product which is then reacted with bromine gas in the absence of oxygen over a silica-alumina catalyst to give the final product.
U.S. Pat. No. 3,591,645 discloses the oxybromination of aromatic compounds, preferably benzene and toluene by heating the substrates in an inert solvent in the presence of bromides and a compound containing nitrate ions. The oxybromination is carried out over a catalyst which is suspended in the solvent and is preferably an oxidizing metal such as copper, manganese, cobalt, vanadium, etc.
Other liquid phase oxybrominations of aromatic compounds are known which use iron or copper salts to effect bromination. See Japanese Nos. 49/18832 and 49/18831. Additionally, the use of molucular sieves to increase para-selectivity in liquid activity phase brominations is described in J. Catal., 60, 110 (1979).
A need still exists, however, for an efficient and selective method for the vapor phase oxybromination of aromatic compounds.